Method for thermal barrier coating and a liner made using said method

ABSTRACT

A method of applying a thermal barrier coating system to a metal piece having cooling holes angled in a first direction and cooling holes angled in a second direction. The method includes spraying a bond coat on a first surface of the piece at angles with respect to the first and second directions and to a thickness selected in combination with the angles to prevent the bond coat from entirely filling any of the holes. A thermal barrier coating is sprayed on the bond coat at angles with respect to the first and second directions and to a thickness selected in combination with the angles to prevent the thermal barrier coating from entirely filling any of the holes. The method also includes spraying a high pressure fluid jet from a nozzle assembly through each hole generally parallel to the respective cooling hole.

BACKGROUND OF THE INVENTION

The present invention relates generally to a method for applying thermalbarrier coatings to metal pieces and the resulting pieces, and moreparticularly to a method for applying a coating system to a gas turbineengine combustion chamber liner having cooling holes and the resultingliner.

Various methods are used to protect metal pieces exposed to hightemperature environments. For instance, cooling air is sometimes blownover the piece. In some applications such as aircraft engine combustionchamber liners, cooling holes are formed in the liner for directing filmcooling air through the liner and over surfaces of the liner exposed tohigh temperatures. The film cooling air cools the liner and forms afluid barrier between the liner and hot gases which flow through theengine to prevent the gases from directly contacting the liner.

In addition, thermal barrier coating systems are applied to surfaces ofmetal pieces exposed to high temperature environments to reduce theamount of heat transferred to the piece. However, applying thermalbarrier coating systems to pieces having cooling holes may cause theholes to become blocked thereby reducing cooling. In order to overcomethis problem, the cooling holes in new pieces are often formed (e.g., bylaser drilling) after the piece is coated. However, forming the coolingholes after the piece is coated generates significant heat which cannegatively affect the life of the piece. To avoid this problem, thecooling holes are sometimes made first and masked before applying thecoating to ensure the holes are not blocked by the coating. However,masking increases the manufacturing cost. Methods of removing coatingsfrom the cooling holes using high pressure fluid jets have beendeveloped to eliminate the need for masking. Although these methods workwell for metal pieces having cooling holes which are angled in a uniformdirection, a method for coating pieces having film cooling holes angledin more than one direction has not been developed.

SUMMARY OF THE INVENTION

Briefly, the present invention includes a method of applying a thermalbarrier coating system to a metal piece having a first plurality ofcooling holes angled in a first direction through the piece from a firstsurface of the piece to a second surface of the piece opposite the firstsurface, and a second plurality of cooling holes angled in a seconddirection different than the first direction through the piece from thefirst surface to the second surface. The method comprises spraying abond coat on the first surface of the piece at angles with respect tothe first direction and the second direction and to a thickness selectedin combination with the angles to prevent the bond coat from entirelyfilling any hole within the first plurality of cooling holes or any holewithin the second plurality of cooling holes. Further, the methodincludes spraying a thermal barrier coating on the bond coat at angleswith respect to the first direction and the second direction and to athickness selected in combination with the angles to prevent the thermalbarrier coating from entirely filling any hole within the firstplurality of cooling holes or any hole within the second plurality ofcooling holes. A high pressure fluid jet is sprayed from a nozzleassembly through each hole within the first plurality of cooling holesin a direction generally parallel to the first direction and througheach hole within the second plurality of cooling holes in a directiongenerally parallel to the second direction.

In another aspect, the invention includes an annular liner for use in acombustor. The liner comprises an annular shell surrounding an axialcenterline having an upstream end, a downstream end, a first pluralityof cooling holes angled in a first direction through the shell from anouter surface to an inner surface, and a second plurality of coolingholes angled in a second direction different than the first directionthrough the shell from the outer surface to the inner surface. Further,the liner includes a thermal barrier coating system applied to the innersurface of the shell. Fluid flow through each of the holes in the firstplurality of cooling holes and the second plurality of cooling holes issubstantially unobstructed by the thermal barrier coating system.

Other features of the present invention will be in part apparent and inpart pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional perspective of a gas turbine enginecombustor of the present invention;

FIG. 2 is a fragmentary view of a portion of a combustor liner taken inthe plane of line 2—2 of FIG. 1;

FIG. 3 is an elevation of a thermal barrier coating spray apparatus usedin the method of the present invention;

FIG. 4 is an elevation of a water jet apparatus used in the method ofthe present invention;

FIG. 5 is a cross section of a piece having a bond coat applied by thethermal barrier coating spray apparatus;

FIG. 6 is a cross section of the piece after the bond coat is removedfrom a cooling hole by the water jet apparatus;

FIG. 7 is a cross section of the piece having a thermal barrier coatingapplied by the thermal barrier coating spray apparatus; and

FIG. 8 is a cross section of a coated piece after the thermal barriercoating is removed from the cooling hole by the water jet apparatus.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings and in particular to FIG. 1, a portion of agas turbine engine, and more particularly a combustor of the presentinvention is designated in its entirety by the reference number 10. Thecombustor 10 defines a combustion chamber 12 in which combustor air ismixed with fuel and burned. The combustor 10 includes an outer liner,generally designated by 14, and an inner liner, generally designated by16. The outer liner 14 defines an outer boundary of the combustionchamber 12, and the inner liner 16 defines an inner boundary of thecombustion chamber. An annular dome, generally designated by 18, mountedupstream from the outer liner 14 and the inner liner 16, defines anupstream end of the combustion chamber 12. Mixer assemblies or mixers 20positioned on the dome 18 deliver a mixture of fuel and air to thecombustor chamber 12. Other features of the combustor 10 areconventional and will not be discussed in further detail.

Although the outer and inner liners 14, 16, respectively, have differentshapes, they have a similar construction. Thus, for brevity only theouter liner 14 will be described in further detail. The outer liner 14includes an annular shell 30 surrounding an axial centerline 32. Theshell 30 has an upstream end 34 which attaches to the combustor dome 18and a downstream end 36 opposite the upstream end. Further, the liner 14has a first or outer surface 38 and a second or inner surface 40opposite the outer surface.

As illustrated in FIG. 2, the liner 14 includes a first plurality ofcooling holes, each of which is designated by 42, extending through theshell 30 from the outer surface 38 to the inner surface 40. Although theholes 42 may extend in other directions without departing from the scopeof the present invention, in one embodiment each of the holes extends ina first direction 44 angled circumferentially about 45 degrees withrespect to the centerline 32 as illustrated in FIG. 2. A secondplurality of cooling holes, each of which is designated by 46, extendsthrough the shell 30 from the outer surface 38 to the inner surface 40in a second direction 48 different than the first direction 44. Althoughthe holes 46 may extend in other directions without departing from thescope of the present invention, in one embodiment the second direction48 has a circumferential component opposite that of the first direction44 and is angled circumferentially about 45 degrees with respect to thecenterline 32. A third plurality of cooling holes, each of which isdesignated by 50, extends through the shell 30 from the outer surface 38to the inner surface 40. Although the holes 50 may extend in otherdirections without departing from the scope of the present invention, inone embodiment each of the holes extends in a third direction 52 angledcircumferentially about 10 degrees with respect to the centerline 32.Although the holes 42, 46, 50 may extend in other directions withoutdeparting from the scope of the present invention, in one embodimenteach of the cooling holes extends axially downstream from the outersurface 38 to the inner surface 40 of the shell 30 at an angle 54 (FIG.5) of about twenty degrees with respect to the inner surface of theshell. In addition to the film cooling holes, the shell 30 also includesa plurality of dilution holes 56 for introducing air into the combustorchamber 20.

Conventionally, all film cooling holes in a liner are oriented in thesame direction. In the present invention, however, different groupingsof the film cooling holes are provided with different circumferentialorientations as explained above to provide an overall hole configurationwhich effectively cools the entire liner 14. As will be understood bythose skilled in the art, the second and third pluralities of coolingholes 46, 50, respectively, are positioned downstream from featureswhich disrupt flow such as the dilution holes 56, borescope holes (notshown), and igniter ports (not shown). The second and third pluralitiesof cooling holes 46, 50 are directed to portions of the liner 14 whichexperienced overheating and burning in prior engine run hardware. Thus,the orientations of the second and third pluralities of cooling holeseliminate or reduce overheating and burning associated with the flowdisrupting features.

In order to reduce heat transfer through the liner 14, a conventionalthermal barrier coating system (i.e., bond coats and thermal barriercoatings), generally designated by 58 (FIG. 7), is applied to the innersurface 40 of the liner 14. Fluid flow through each of the cooling holes42, 46, 50 is substantially unobstructed by the thermal barrier coatingsystem 58. Other features of the liner 14 are conventional and will notbe discussed in further detail. With the exception of applying thethermal barrier coating system 58 to the liner 14, the liner is made byconventional methods which will not be described in detail.

To apply the thermal barrier coating system 58, the liner 14 ispositioned on a conventional turntable, generally designated by 60,having a support 62 sized and shaped for receiving the liner and acentral vertical shaft 64 for rotating the support as illustrated inFIG. 3. A conventional thermal barrier coating spray apparatus,generally designated by 70, is provided adjacent the turntable 60 forapplying the thermal barrier system 58 to the inner surface 40 of theliner. The apparatus 70 includes a spray head 72 having a nozzle 74through which the thermal barrier system is sprayed and a robotic arm 76for manipulating the head into position relative to the liner 14.Although other apparatus may be used without departing from the scope ofthe present invention, the thermal barrier coating spray apparatus 70 ofthe preferred embodiment is an ATCS plasma system with an 8-axiscomputer numerically controlled Fanuc robot system available from SulzerMetco of Westbury, N.Y.

FIG. 4 illustrates the liner 14 received by another conventionalturntable, generally designated by 80, comprising a support 82 and acentral vertical shaft 84 for rotating the support. A conventional waterjet apparatus, generally designated by 90, adjacent the turntable 80sprays water toward the outer surface 38 of the liner 14. The water jetapparatus 90 includes a spray head 92 having a nozzle 94 for spraying ahigh pressure jet of fluid such as water toward the liner and a roboticarm 96 for manipulating the head into position relative to the liner 14.Although other apparatus may be used without departing from the scope ofthe present invention, the water jet apparatus 90 of the preferredembodiment is a Model No. 1015 5-axis computer numerically controlledwater jet system available from Progressive Technologies of GrandRapids, Mich. As the previously described thermal barrier coating sprayapparatus 70 and water jet apparatus 90 are conventional and wellunderstood by those skilled in the art, they will not be described infurther detail.

As described above, the liner 14 includes several pluralities of coolingholes 42, 46, 50. As illustrated in FIG. 5, each of these cooling holes(only one of which is shown) is defined by a tubular surface 100. Eachcooling hole extends along a central axis 102 through the liner 14 fromthe outer surface 38 of the liner to the inner surface 40. The centralaxis 102 of each hole is oriented at the aforementioned angle 54 (e.g.,twenty degrees) with respect to the inner surface 40 of the liner 14.The size of the hole is not critical to the present invention.

As further illustrated in FIG. 5, the thermal barrier coating sprayapparatus 70 sprays a bond coat 110 such as NiCrAlY on the inner surface40 of the liner 14 at a spray angle 112 measured with respect to thecentral axis 102 of the hole and to a thickness 114 selected incombination with the angle 112 to prevent the bond coat from entirelyfilling the hole. Although the spray angle 112 may vary withoutdeparting from the scope of the present invention, the angle 112 ispreferably greater than ninety degrees (i.e., obtuse) to minimize theamount of bond coat sprayed on the surface 100 defining the holeopposite the spray nozzle 76. Further, the bond coat 110 is preferablysprayed on the inner surface 40 at an angle of incidence 116 measuredwith respect to the first surface of at least about 45 degrees. Anglesof incidence 116 less than about 45 degrees tend to cause the coat 110to have unmelted areas, voids and lower tensile strength.

As previously mentioned, the spray angle 112 and the thickness 114 areselected in combination to prevent the bond coat from entirely fillingthe hole. For example, for a liner 14 having nominal 0.020 to 0.030 inchdiameter holes extending at an angle 54 of approximately twenty degrees,the bond coat 110 may be sprayed on the inner surface 40 at an angle ofincidence 116 of about 45 degrees and an angle 112 with respect to thecentral axis 102 of the hole of about 135 degrees. Further, the bondcoat 110 is sprayed to a thickness 114 of between about 0.004 inches andabout 0.010 inches, and more preferably to a thickness of between about0.004 inches and about 0.006 inches. As will be appreciated by thoseskilled in the art, the angles and thickness may be varied withoutdeparting from the scope of the present invention. However, it isdesirable that the angle 112 measured with respect to the central axis102 and the thickness 116 be selected so that the bond coat does notentirely fill the hole. The unfilled portion of the hole provides apilot hole so that the water jet apparatus can remove the bond coat 110from the hole as will be explained below.

Although the spray angle 112 and thickness 114 specified above have beenfound to be effective to prevent the bond coat 110 from entirely fillingthe holes 42, 46, 50, those skilled in the art will appreciate thatconsiderable process simplification can be accomplished by maintaining aconstant angle of incidence 116 and allowing the spray angle to varybetween the first, second and third pluralities of cooling holes. Forexample, for a liner 14 having cooling holes 42, 46, 50 oriented asspecified above, it has been found that the bond coat 110 may be appliedin a direction having no circumferential component and at an angle ofincidence 116 of about 45 degrees downstream. For liners 14 having othercooling hole orientations, the spray angle 112 and thickness 114 may bedetermined by trial and error.

After the bond coat 110 is applied, the liner 14 is placed on theturntable support 80 adjacent the water jet apparatus 90. As shown inFIG. 6, the water jet apparatus 90 sprays a high pressure water jettoward the hole from a nozzle 96 facing the outer surface 38 of theliner 14 and in a direction 118 generally parallel to the central axis102 of the hole. Unlike the bond coat 110 which can be applied at aconstant angle of incidence 116 to simplify the process, the highpressure water jet must be aimed in a direction generally parallel tothe first direction 44 when spraying the high pressure fluid jet througheach hole within the first plurality of cooling holes 42, aimed in adirection generally parallel to the second direction 48 when sprayingthe high pressure fluid jet through each hole within the secondplurality of cooling holes 46, and aimed in a direction generallyparallel to the third direction 52 when spraying the high pressure fluidjet through each hole within the third plurality of cooling holes 50.

The water jet is substantially free of solid particulate so the jetremoves only the bond coat 110 from the hole 102 without removing metalfrom the liner 14. As previously mentioned, a pilot hole is needed topermit the water jet to remove the bond coat 110 from the hole. This isbecause the water jet abrades the bond coat 110 rather than pushing itfrom the hole. If the pilot hole is not present, the abrasion capabilityof the water jet is reduced. Although the water jet may be sprayed atother pressures without departing from the scope of the presentinvention, the water jet apparatus of the preferred embodiment producesa water jet having a pressure of between about 5000 pounds per squareinch and about 50,000 pounds per square inch. Preferably, the water jetis sprayed from the nozzle 96 at a pressure of about 45,000 pounds persquare inch.

After the bond coat 110 is removed from the hole, the liner 14 isreturned to the first turntable 110. As illustrated in FIG. 7, thethermal barrier coating spray apparatus 70 sprays a thermal barriercoating 120 such as yttria stabilized zirconia on the bond coat 110 at aspray angle 122 measured with respect to the central axis 102 of thehole and to a thickness 124 selected in combination with the angle atwhich the thermal barrier coating is sprayed to prevent the thermalbarrier coating from entirely filling the hole. Further, the thermalbarrier coating 120 is preferably sprayed on the bond coat 110 at anangle of incidence 126 with respect to the bond coat surface of at leastabout 45 degrees. Angles of incidence 126 less than about 45 degreestend to cause the coating 120 to have unmelted areas, voids and lowertensile strength.

As with the bond coat parameters, the spray angle 122 and the thickness124 are selected in combination to prevent the thermal barrier coatingfrom entirely filling the hole. For example, for the previouslydescribed liner 14 having nominal 0.020 to 0.030 inch diameter holesextending through the liner at an angle 54 of approximately twentydegrees, the thermal barrier coating 120 may be sprayed on the bond coat110 at an angle of incidence 126 of about 45 degrees and a spray angle122 of about 135 degrees. Further, the coating 120 is sprayed in atleast one coat having a thickness 124 of between about 0.003 inches andabout 0.015 inches. Preferably, the coating 120 is sprayed in a coathaving a thickness 124 of about 0.010 inches. As will be appreciated bythose skilled in the art, the angles and thickness may be varied withoutdeparting from the scope of the present invention. However, it isdesirable that the spray angle 122 and the thickness 124 be selected sothat the coating 120 does not entirely fill the hole. As with the bondcoat, leaving a pilot hole in the thermal barrier coating enables thewater jet to remove the coating 120 from the hole.

Although the spray angle 122 and thickness 124 specified above have beenfound to be effective to prevent the thermal barrier coating 120 fromentirely filling the holes 42, 46, 50, those skilled in the art willappreciate that considerable process simplification can be accomplishedby maintaining a constant angle of incidence 126 and allowing the sprayangle to vary between the first, second and third pluralities of coolingholes. For example, for a liner 14 having cooling holes 42, 46, 50oriented as specified above, it has been found that the thermal barriercoating 120 may be applied in a direction having no circumferentialcomponent and at an angle of incidence 126 of about 45 degreesdownstream. For liners 14 having other cooling hole orientations, thespray angle 122 and thickness 124 may be determined by trial and error.

After the thermal barrier coating 120 is applied, the liner 14 is placedon the turntable support 80 adjacent the water jet apparatus 90 (FIG.4). The water jet apparatus 90 sprays a high pressure water jet towardthe hole from the nozzle 96 facing the outer surface 38 of the liner 14and in a direction 118 generally parallel to the central axis 102 of thehole to remove thermal barrier coating from the hole. Because the waterjet is substantially free of solid particulate, the jet only removes thethermal barrier coating 120 from the hole without removing metal fromthe liner 14. Although the water jet pressure may vary without departingfrom the scope of the present invention, in the preferred embodiment thewater jet pressure used during this spraying step is identical to thepressure used during the prior spraying step.

After the thermal barrier coating 120 is removed from the hole,additional layers of thermal barrier coating (not shown) may be appliedto the liner 14 to build the total coating thickness. Preferably, thecoating 120 is removed from the hole after applying each layer. As willbe appreciated by those skilled in the art, the step of spraying theliner with the water jet after the bond coat 110 is applied and beforethe thermal barrier coating 120 is applied may be omitted if thecombined thickness of the layers is thin enough that they do notentirely fill the hole thereby allowing the layers to be removedtogether.

Because the water jet does not damage the base metal of the liner 14,its flow need not be interrupted as the jet travels from hole to hole.Further, where the liner 14 has a series of holes, either the liner orthe water jet nozzle 96 (or both) may be moved with respect to the otherto sequentially align the water jet with each of the holes in theseries. For example, where the liner 14 is circular and the series ofholes is oriented in a row extending circumferentially around the liner,the liner may be rotated to move the liner with respect to the nozzle 96and to align the nozzle with each hole of the series. A motor (notshown) connected to the shaft 84 may be used to continuously rotate theturntable 80 and liner 14. Although the liner 14 and the nozzle 96 maybe moved at other rates without departing from the scope of the presentinvention, in the preferred embodiment they are moved at a relativespeed of between about twenty inches per minute and about 480 inches perminute. In a particularly preferred embodiment, the liner 14 is movedrelative to the nozzle 96 at a rate of about twenty inches per minute.Although the turntable 80 of the preferred embodiment rotatescontinuously, it is envisioned that the turntable may be rotatedintermittently so the water jet dwells when aligned with each hole.

The method of using the water jet apparatus of the second embodiment 90is similar to that described above with respect to the water jetapparatus of the first embodiment 90. As illustrated in FIG. 3, a bondcoat 110 is sprayed on the metal work liner 14 at an angle 116 and to athickness 114 selected to prevent the bond coat from entirely fillingthe hole 84. The water jet apparatus 90 is used to spray a high pressurefluid jet in a direction generally parallel to the central axis 102 ofthe cooling holes 84 to remove bond coat 110 from them. After the bondboat 110 is removed from the holes 84, a thermal barrier coating 120 issprayed on the bond coat 110 as shown in FIG. 5 at an angle 126 and to athickness 124 selected to prevent the thermal barrier coating fromentirely filling the hole 84. The step of spraying the high pressurefluid jet is repeated to remove thermal barrier coating 120 from thecooling holes 84.

Although the fluid jet may be sprayed at other pressures withoutdeparting from the scope of the present invention, in one embodiment thefluid jet is sprayed from the nozzle orifice 112 at a pressure ofbetween about 5000 pounds per square inch and about 50,000 pounds persquare inch, and more particularly, at a pressure of about 45,000 poundsper square inch. Although the orifice 112 of the nozzle assembly 90 maybe spaced from the liner 14 by other distances without departing fromthe scope of the present invention, in one embodiment the orifice of thenozzle assembly is spaced from the metal liner by a distance 122 ofbetween about 0.1 inches and about 3 inches as shown in FIG. 7 while thefluid jet is sprayed from the nozzle assembly. Further, it is envisionedthat it may be beneficial that the orifice 112 of the nozzle assembly 90be spaced from the liner 14 by a distance 122 of between about 0.8inches and about 1.6 inches while the jet is sprayed from the assembly.

In addition, although the orifice 112 may be moved relative to the linerat other speeds without departing from the scope of the presentinvention, in one embodiment the orifice of the nozzle assembly 90 ismoved relative to the liner 14 at a speed of between about 20 inches perminute and about 480 inches per minute as the fluid jet is sprayed fromthe nozzle assembly. It is further envisioned that it may be beneficialto move the orifice 112 relative to the liner 14 at a speed of about 240inches per minute as the fluid jet is sprayed from the nozzle assembly90. Although the nozzle assembly 90 may be aligned in other orientationswithout departing from the scope of the present invention, in oneembodiment the nozzle assembly is aligned generally parallel to thesecond surface 22 of the liner 14 while the jet is sprayed from theassembly 90.

As will be appreciated by those skilled in the art, in addition tocombustion chamber liners such as those described above, the presentinvention is applicable to other metal pieces having coatings andcooling holes extending in more than one direction. In addition, thoseskilled in the art will appreciate that the liner 14 may be a new linerwhich has never had a thermal barrier coating system or it may be arepaired liner from which damaged thermal barrier coating has beenremoved by conventional mechanical and/or chemical stripping processes.

When introducing elements of the present invention or the preferredembodiment(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

As various changes could be made in the above constructions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. A method of applying a thermal barrier coatingsystem to a metal piece having a first plurality of cooling holes angledin a first direction through the piece from a first surface of the pieceto a second surface of the piece opposite the first surface, and asecond plurality of cooling holes angled in a second direction differentthan said first direction through the piece from the first surface tothe second surface, said method comprising the steps of: spraying a bondcoat on said first surface of the piece at angles with respect to saidfirst direction and said second direction and to a thickness selected incombination with the angles to prevent the bond coat from entirelyfilling any hole within said first plurality of cooling holes or anyhole within said second plurality of cooling holes; spraying a thermalbarrier coating on the bond coat at angles with respect to said firstdirection and said second direction and to a thickness selected incombination with the angles to prevent the thermal barrier coating fromentirely filling any hole within said first plurality of coding holes orany hole within said second plurality of cooling holes; and spraying ahigh pressure fluid jet from a nozzle assembly through at least one holewithin said first plurality of cooling holes in a direction generallyparallel to said first direction to remove at least one of said bandcoat and said thermal barrier coating from said at least one hole withinsaid first plurality of cooling holes.
 2. A method as set forth in claim1 wherein the step of spraying the high pressure fluid jet from thenozzle assembly is performed at least twice, once after the step ofspraying the bond coat but before the step of spraying the thermalbarrier coating to remove the bond coat from said first plurality ofholes and said second plurality of holes, and again after the step ofspraying the thermal barrier coating to remove the thermal barriercoating from said first plurality of holes and said second plurality ofholes.
 3. A method as set forth in claim 1 wherein the thermal barriercoating is sprayed on said first surface in at least two coats and thestep of spraying the fluid from the nozzle assembly is performed atleast twice, once after spraying a first coat of said coats of thermalbarrier coating and again after spraying a second coat of said coats ofthermal barrier coating.
 4. A method as set forth in claim 1 wherein thefluid jet is sprayed from the nozzle assembly toward the second surfaceof the metal piece.
 5. A method as set forth in claim 1 wherein thefluid jet is sprayed from the nozzle assembly at a pressure of betweenabout 5000 pounds per square inch and about 50,000 pounds per squareinch.
 6. A method as set forth in claim 6 wherein the fluid jet issprayed from the nozzle assembly at a pressure of about 45,000 poundsper square inch.
 7. A method as set forth in claim 1 wherein the nozzleassembly is spaced from the metal piece by a distance of between about0.8 inches and about 1.6 inches while the jet is sprayed from theassembly.
 8. A method as set forth in claim 1 further comprising thestep of moving the nozzle assembly relative to the metal piece at aspeed of between about 20 inches per minute and about 480 inches perminute as the fluid jet is sprayed from the nozzle assembly.
 9. A methodas set forth in claim 1 wherein the step of spraying the high pressurefluid jet further comprises spraying the high pressure fluid jet fromthe nozzle assembly through at least one hole within said secondplurality of cooling holes in a direction generally parallel to saidsecond direction to remove at least one of said bond coat and saidthermal barrier coating from said at least one hole within said secondplurality of cooling holes.
 10. A method as set forth in claim 9 whereinthe high pressure fluid jet is sprayed through each hole within thefirst plurality of cooling holes and through each hole with the secondplurality of cooling holes during the step of spraying the high pressurefluid jet.
 11. A method as set forth in claim 10 wherein the nozzleassembly sprays the high pressure fluid jet through each hole in saidfirst plurality of cooling holes generally parallel to said firstdirection and through each hole in said second plurality of coolingholes generally parallel to said second direction.
 12. A method ofapplying a thermal barrier coating system to an annular linersurrounding an axial centerline and extending between an upstream endand a downstream end, said liner having a first plurality of coolingholes angled in a first hole direction through the liner from an outersurface to an inner surface, and a second plurality of cooling holesangled in a second hole direction through the liner from the outersurface to the inner surface, said second hole direction having acircumferential component opposite that of said first hole direction,said method comprising the steps of: spraying a bond coat on the innersurface in a first spray direction having an axial component to athickness selected in combination with the first spray direction toprevent the bond coat from entirely filling any hole within said firstplurality of cooling holes or any hole within said second plurality ofcooling holes; spraying a thermal barrier coating on the bond coat in asecond spray direction having an axial component to a thickness selectedin combination with the second spray direction to prevent the thermalbarrier coating from entirely filling any hole within said firstplurality of cooling holes or any hole within said second plurality ofcooling holes; and spraying a high pressure fluid jet from a nozzleassembly through at least one hole within said first plurality ofcooling holes in a direction generally parallel to said first directionto remove at least one of said bond coat and said thermal barriercoating from said at least one hole with in said first plurality ofcooling holes.
 13. A method as set forth in claim 12 wherein said firstplurality of cooling holes and said second plurality of cooling holesare angled axially downstream from the outer surface to the innersurface, and the bond coat and the thermal barrier coating are sprayedaxially upstream toward the inner surface of the liner.
 14. A method asset forth in claim 12 wherein the liner has a third plurality of coalingholes angled axially downstream through the liner from the outer surfaceto the inner surface, and the bond coat and the thermal barrier coatingare sprayed axially downstream toward the inner surface of the liner.15. A method as set forth in claim 12 wherein the step of spraying thehigh pressure fluid jet from the nozzle assembly is performed at leasttwice, once after the step of spraying the bond coat but before the stepof spraying the thermal barrier coating to remove the bond coat fromsaid first plurality of holes and said second plurality of holes, andagain after the step of spraying the thermal barrier coating to removethe thermal barrier coating from said first plurality of holes and saidsecond plurality of holes.
 16. A method as set forth in claim 12 whereinthe thermal barrier coating is sprayed on the inner surface in at leasttwo coats and the step of spraying the fluid from the nozzle assembly isperformed at least twice, once after spraying a first coat of said coatsof thermal barrier coating and again after spraying a second coat ofsaid coats of thermal barrier coating.
 17. A method as set forth inclaim 12 wherein the fluid jet is sprayed from the nozzle assemblytoward the outer surface of the liner.
 18. A method as set forth inclaim 12 wherein the step of spraying the high pressure fluid jetfurther comprises spraying the high pressure fluid jet from the nozzleassembly through at least one hole within said second plurality ofcooling holes in a direction generally parallel to said second spraydirection to remove at least one of said bond coat and said thermalbarrier coating from said at least one hole within said second pluralityof cooling holes.
 19. A method as set forth in claim 18 wherein the highpressure fluid jet is sprayed through each hole within the firstplurality of cooling holes and through each hole with the secondplurality of cooling holes during the step of spraying the high pressurefluid jet.
 20. A method as set forth in claim 19 wherein the nozzleassembly sprays the high pressure fluid jet through each hole in saidfirst plurality of cooling holes generally parallel to said first spraydirection and through each hole in said second plurality of coolingholes generally parallel to said second direction.